1. Field of the Invention
This invention relates to motor gasoline compositions suitable for use in automotive vehicles.
2. Prior Art
Spark plugs are susceptible to fouling in automobile engines particularly where lead-free gasoline is used. Plug fouling is the phenomenon in which the spark plugs are covered with deposits at their insulator legs and electrodes and which is more likely to occur during cold winter season. Plug fouling causes starting difficulty and unstable operation of the engines at low speed, and further invites insufficient acceleration.
It is known that plug fouling takes place more frequently the higher in aromatics contents and the heavier the lead-free gasoline.
This problem has been coped with by using spark plugs of high quality as regards their construction and thermal value, or by avoiding prolonged operation of engines in an excessively rich air-fuel mixture. A keen demand has been voiced for improved means capable of protecting spark plugs from fouling without resort to modifications of the construction and operation of spark plugs per se.
As stated above, lead-free gasoline fuels of a composition having high aromatics content and heavy characteristics are responsible for fouled spark plugs in the automobile engine. Although the gasoline composition of the invention is also similar in these characteristics, it has now been found that the same gasoline composition when admixed with specific phthalate diesters can eliminate spark plug fouling.
In the meantime, agents other than conventional alkylated lead have been proposed to increase the octane number of motor gasolines. It has also been proposed to this end to modify the hydrocarbon composition of gasoline itself, for example with use of high aromatic components so as to attain an octane number as high as 95 or even higher than 98. The gasoline composition of the invention can be of this high octane class, and yet is free from spark plug fouling.
The present invention seeks to provide a novel gasoline composition which is effective in particular for inhibiting spark plug fouling.
This and other objects and advantages of the invention can be achieved by the provision of a gasoline composition for automotive fuel which comprises a gasoline fraction having an aromatics content of greater than 35 volume percent and a 50 percent distillation temperature of 85.degree. to 125.degree. C., and a specified amount of a selected phthalate diester.